U.S. Pat. No. 6,017,926 (issued Jan. 25, 2000) discloses the compound of structural formula I: 
Compound I is an antagonist of the integrin xcex1vxcex23 receptor and is useful for inhibiting bone resorption, restenosis, angiogenesis, diabetic retinopathy, macular degeneration, inflammatory arthritis, cancer, and metastatic tumor growth. It is particularly useful for inhibiting bone resorption and for the treatment and prevention of osteoporosis. There is no specific disclosure or discussion in U.S. Pat. No. 6,017,926 of crystalline forms of compound I. A novel process for the preparation of compound I was disclosed in WO 01/34602 (May 17, 2001). The latter process yielded compound I in the form of a crystalline hemihydrate as characterized by differential scanning calorimetry, X-ray powder diffraction, and FT-infrared spectroscopy. However, the sensitivity of the hemihydrate form to moisture complicates the development of solid dosage formulations for compound I. It is therefore desirable to have available other crystalline forms of compound I having improved physical and chemical stability and hence greater suitability for the preparation of solid pharmaceutical dosage forms containing the pharmacologically active ingredient.
The present invention is concerned with novel crystalline forms of the integrin xcex1vxcex23 receptor antagonist 3-{2-oxo-3-[3-(5,6,7,8-tetrahydro-[1,8]naphthyridin-2-yl)-propyl]imidazolidin-1-yl}-3(S)-(6-methoxy-pyridin-3-yl)-propionic acid (I). These crystalline forms are new and may have advantages in the preparation of pharmaceutical compositions of compound I, such as ease of processing, handling, or dosing. In particular, they may improved physiochemical properties such as solubility, stability, or rate of solution, rendering them particularly suitable for the manufacture of dosage forms. The invention also concerns pharmaceutical compositions containing the novel crystalline forms as well methods for using them as xcex1vxcex23 integrin receptor antagonists.